EARTH ROTATION 9 opinion appears nevertheless satisfactory, since planets cannot have two motions at once and the objection, that lofty things would fall, is contradicted; for every way the under part of the Earth is also the upper; since wherever the spectator stands on the Earth's surface, even that spot is the uppermost spot.¹ Earth rotation by a current of aerial fluid It is very interesting to see the theory once advocated by Herakleides of Pontus transplanted on Indian soil, especially when we remember that Seleukus, the Babylonian, had adopted that theory. From Babylon the theory might easily find its way to India, though it is of course equally possible that Aryabhata, quite independently of his Greek precursors, hit on the same idea. He appears to have accounted for the Earth's rotation by a wind or current of aerial fluid, the extent of which, according to the orbit assigned to it by him, corresponds to an elevation of little more than a hundred miles (114) from the surface of the Earth, or fifteen yojana's while he put the diameter of the Earth equal to 1050 yojanas (of 7.6.miles each). This was in accordance with the general opinion of the Indians, that the planets are carried along their orbits by mighty winds with the same velo- city and parallel to the ecliptic (while one great vortex carries all stars round the Earth in twenty-four hours, but that the planets are deflected from these courses by certain invisible powers having hands and reins, with which they draw the planets out of their uniform progress. The power at the apogee, for instance constantly attracts the planet towards itself, alternately with the right and left hand (like Lachesis in Plato's Republic), while the deity at the node diverts the planet from the ecliptic first to one side and then to the other. And lastly the deity at the con- junction causes the planet to move with variable velocity and to become occasionally stationary and even retrograde. This is gravely set forth in the Surya-siddhanta ,and even Bhaskara gives the theory in his notes, though he omits it from his text. Similarly Brahmagupta, although he gives the theory of eclipses, affirms the existence of an eighth planet, Rahu, which is the immediate cause of eclipses; and he blames Varahamihira, 1. Asiat. Res, XII. p. 227; Colebrooke's Essays, II. p. 392, 2. Colebrooke, Notes and Illustrations to the Algebra of Brahmagupta, p. xxxviii. Essays. II. p. 467.
